Help¶

When selected, the scheduler ready queue will be implemented as the classic/textbook array of lists, one per priority (max 32 priorities). This corresponds to the scheduler algorithm used in Zephyr versions prior to 1.12. It incurs only a tiny code size overhead vs. the “dumb” scheduler and runs in O(1) time in almost all circumstances with very low constant factor. But it requires a fairly large RAM budget to store those list heads, and the limited features make it incompatible with features like deadline scheduling that need to sort threads more finely, and SMP affinity which need to traverse the list of threads. Typical applications with small numbers of runnable threads probably want the DUMB scheduler.

Direct dependencies¶

!SCHED_DEADLINE && <choice SCHED_ALGORITHM: Scheduler priority queue algorithm>

(Includes any dependencies from ifs and menus.)

Kconfig definition¶

At <Zephyr>/kernel/Kconfig:251

Included via <Zephyr>/Kconfig:8 → <Zephyr>/Kconfig.zephyr:30

Menu path: (Top) → General Kernel Options → Scheduler priority queue algorithm

config SCHED_MULTIQ
    bool "Traditional multi-queue ready queue"
    depends on !SCHED_DEADLINE && <choice SCHED_ALGORITHM: Scheduler priority queue algorithm>
    help
      When selected, the scheduler ready queue will be implemented
      as the classic/textbook array of lists, one per priority
      (max 32 priorities).  This corresponds to the scheduler
      algorithm used in Zephyr versions prior to 1.12.  It incurs
      only a tiny code size overhead vs. the "dumb" scheduler and
      runs in O(1) time in almost all circumstances with very low
      constant factor.  But it requires a fairly large RAM budget
      to store those list heads, and the limited features make it
      incompatible with features like deadline scheduling that
      need to sort threads more finely, and SMP affinity which
      need to traverse the list of threads.  Typical applications
      with small numbers of runnable threads probably want the
      DUMB scheduler.

(The ‘depends on’ condition includes propagated dependencies from ifs and menus.)